Patent GB-707634-A (GB)
Title: Magnetic storage systems
Inventor: WILLIAMS FREDERIC CALLAND
IPC: H04L25/04
Filed: 1949-03-01
Abstract: 707,634. Digital electric calculating apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 16, 1950 [March 1, 1949], No. 5632/49. Class 106 (1) A magnetic storage system for storing electrical signals of two kinds comprises means for recording each signal within a discrete length of a track on a magnetic recording medium as a predetermined pattern of magnetization in which the orientation of the magnetization in one part of the discrete length is substantially in a first direction along the track and the orientation of the magnetization in the other part of the discrete length is substantially in a second and opposite direction, an abrupt reversal occurring at some intermediate point, a signal of one kind being represented by a reversal in one sense and a signal of the other kind being represented by a reversal in the opposite sense. In the described embodiment the invention is applied to a rotating magnetic drum of the type described in Specification 707,635, synchronized with and forming a data storage unit of an electronic computing machine of the type described in Specification 705,479. A binary pulse train, e.g. 1011, from the computor CRT store 2, Fig. 4, is gated, under control of a voltage on a terminal 4, and is applied at the appropriate time to a diode D4 of a coincidence circuit. An inverted form of the signal arrives at a diode D7 via an inverter 43 and cathode follower 44. A series of negativegoing trigger pips, Fig. 5(b), derived from the leading edges of the digit square wave, Fig. 5(a), are fed to the other diodes D3, D8 of the coincidence circuits, so that the waveform passed through a diode D5 to the grid of valve V4 is as shown in Fig. 5(e), while that passed by diode D6 to the grid of valve V5 is as shown in Fig. 5(g). A series of trigger pips, Fig. 5(c), derived from the trailing edges of the digit square wave, Fig. 5(a), are fed to the anodes of valves V4 and V5, the changes of state of this flip-flop providing a signal (e.g. at the anode of V5 the waveform h, Fig. 5) which, through push-pull amplifiers, two successive step-down transformers and a writing head, lays down a pattern of magnetization, Fig. 5(i), in which the binary " one " is represented by a reversal of magnetization in one sense and a binary " O " by a reversal in the opposite sense. The response waveform from the reading head indicated in Fig. 8(b), is amplified and applied via a resistor R51, Fig. 7, to the grid of a valve V21 giving rise to a squared waveform, Fig. 8(c), at the grid of the valve V22. The suppressor of valve V22 receives a fine strobe or marker pulse, Fig. 8(e), from a valve V23 which is controlled by the dash waveform generator 20. If the control grid of valve V22 is negative when the strobe pulse is applied the anode is maintained at 50V via a crystal G2: if the grid is positive, the negative spike produced at its anode pulls a condenser C58 down to +10V through a diode D22, the condenser remaining at this potential until it is pulled back to +50V, the negative dash waveform generated in valve V24. The resultant output signal, Fig. 8(f), is equivalent to the input signal, Fig. 5(d), but with a slight delay which is accounted for by the actual distance between the writing and reading head gaps at the surface of the drum.